The invention relates to a rotary drum having a toothed rim which is arranged on the drum casing and supported at a number of points on the periphery of the drum casing by means of a bridge member which contains two axially spaced clips which are welded to the drum casing and a cross plate which connects the clips and is arranged radially distant from the drum casing.
A rotary drum of the type described can be constructed for various applications, such as a rotary dryer, mixing drum, tube mill, rotating cylinder for a rotary kiln, etc. Such a drum is driven by the toothed rim arranged on the drum casing, the teeth of the rim engaging with at least one drive gear.
In one known construction of the type described each cross plate of a bridge member has both ends welded onto the corresponding clip, whilst the toothed rim is supported on the central region of the cross plates and screwed in position there.
In rotary drums which are intended for heat treatment of any material placed inside them and are therefore heated from inside in any manner, the drum casing is necessarily heated during the heat treatment to a temperature which, because of the radial spacing of the toothed rim from the drum casing, is markedly higher than the temperature of the toothed rim. As the resulting radial thermal expansion of the drum casing is greater than that of the toothed rim, this can give rise to undesirable bowing and deformation of the cross plates which are fixed to the clips. However, it should be borne in mind that each cross plate is at a specific radial distance from the kiln casing and is not therefore so greatly heated as the drum casing, with the result that the drum casing expands more in the axial direction than does the cross plate. These differing degrees of thermal expansion lead to further strain on the cross plates, the clips and the welded connections.